Vehicles of the type using a gasoline engine as a drive source are chiefly available at present. However, vehicles of the type using an electric motor as a drive source are required at locations where the occurrence of an exhaust gas must be avoided. A motor-driven vehicle, however, has an inconvenience in that it has an increased body weight and a shortened running distance. To cope with such an inconvenience, there is an increased demand that a hybrid vehicle including an electric motor in addition to an engine be developed.
Japanese Patent Laid-Open Publication No. HEI-8-175477, for example, discloses a hybrid motorcycle entitled `DEVICE FOR SWITCHING ENGINE POWER TO/FROM MOTOR POWER IN MOTORCYCLE OR THE LIKE`.
As shown in FIG. 2 of the above publication, a crank shaft is parallel to an axle, and as shown in FIG. 3, a shaft of a motor is perpendicular to the axle.
To be more specific, according to the related art structure, since the crank shaft extends in the lateral direction of a vehicular body and the shaft of the motor extends in the longitudinal direction of the vehicular body, a transmission case which contains both the crank shaft and the shaft of the motor is applied with forces both in the lateral and longitudinal directions.
Accordingly, the transmission case must be rigid enough to withstand the above forces both in the lateral and longitudinal directions, which requires an not only increase in the weight of power the transmission case but also causes a loss of power transmission in the power transmission system.